In imaging systems commonly used today, a charge retentive surface on a charge retentive member is typically charged to a uniform potential and thereafter exposed to a light source to selectively discharge the charge retentive surface and form a latent electrostatic image thereon. The latent image may comprise either the discharged portions or the charged portions of the charge retentive surface. The light source may comprise any well known device such as a light lens scanning system, a laser beam or an array of LEDs. Subsequently, the electrostatic latent image on the charge retentive surface is rendered visible by developing the image with developer powder. The most common development systems employ developer powder which includes both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the charge retentive surface to form a powder image thereon. The developed toner image is transferred to a support surface on a receiver sheet such as a plain paper sheet to which it may be permanently affixed by heating or by the application of pressure or a combination of both.
In order to fix or permanently fuse the toner material onto the receiver sheet by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the receiver sheet or otherwise upon the surfaces thereof. Thereafter, as toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the receiver sheet.
One approach to thermal fusing of toner material images onto the receiver sheet has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which, called the fuser roll, is heated. During operation of a fusing system of this type, the receiver sheet to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the heated fuser roll thereby effecting the heating of the toner images within the nip. Such fusing devices typically comprise two rollers wherein the fusing roller is coated with an abhesive material, such as a silicone rubber or other low surface energy elastomer or, for example, tetrafluoroethylene resin sold by E.I. duPont de Nemours and Company under the trademark TEFLON®. In these fusing systems, however, since the toner image is tackified by heat, a part of the image carried on the surface of the fuser roll adheres to the fuser roll and is offset either to a subsequent receiver sheet or to the pressure roll when there is no sheet passing through a fuser nip. Both types of offset may contaminate the pressure roll with subsequent offset of toner from the pressure roll to the image substrate.
To solve the foregoing toner offset problem it has been common practice to utilize toner release agents such as silicone oil, in particular polydimethyl silicone oil, which is applied to the fuser roll surface to a thickness of the order of about one micron to act as a toner release material. Such release agent materials possess a relatively low surface energy and have been found suitable for use in the heated fuser roll environment. In practice, a thin layer of silicone oil is applied to the surface of the heated roller to form an interface between the roller surface and the toner image carried on the support material. This provides a surface with a low surface energy that is easily parted from the toner when the toner passes through the fuser nip and thereby prevents toner from adhering to the fuser roll.
Various systems have been used to deliver release agent fluid to the roll. Such systems incorporate oil soaked rolls and wicks with and without supply sumps as well as oil impregnated webs. Another type of release agent management system holds release agent material in a sump from which it is dispensed using a metering roll and a donor roll, the former of which contacts the release agent material and the latter of which contacts the surface of the heated fuser roll. As such, the problem to be solved is the delivery of release oil in carefully measured amounts to the fuser roller so that the release agent oil delivered is sufficient to release the toner from the fuser roller yet not so much as to carry over to the receiver sheet.